1. Field of the Invention
The present application relates in general to a printing apparatus. More particularly, the present application relates to sheet feeding systems for the printing apparatus.
2. Description of the Related Art
In conventional ink jet printing apparatus ink jet printing is generally performed by discharging ink from a plurality of nozzles of an ink jet printing head onto a recording medium or sheet as the sheet is fed past the printing head. However, as the sheet is being fed toward the printing head the leading and trailing edges of the sheet have a tendency to curve or float so that the quality of the image being formed at the edges is lower than the quality of the image formed on the rest of the sheet. Further, in such conventional ink jet printing apparatus, when ink drops discharged onto the sheet penetrate into the fibers of the sheet, the fibers become moist and expand so that the sheet may partially wrinkle, curve and/or float causing the sheet to contact the printing head. If the sheet contacts the printing head the quality of the image being printed may be affected.
One technique conventional ink jet printing apparatus used to avoid the problems caused when the sheet wrinkles, curves or floats was to reduce the area of the sheet that could be printed on so no printing occurred close to the edges.
Another technique for avoiding these problems is discussed in Japanese Laid Open patent Application Number 07-17088. In the '088 publication the sheet is grasped by a feeding roller and a pinch roller in contact with the feeding roller and an ejecting roller, and by a spur in contact with the ejecting roller. However, in this technique a trailing edge of the sheet curves upward or floats after the trailing edge passes a gap between the feeding roller and the pinch roller so that suitable printing of an image on the trailing edge of the sheet cannot be achieved.
Another technique for avoiding these problems is discussed in Japanese Laid Open patent Application No. 17-266570. In the '570 publication a sheet is pre-heated and then is fed by a feeding belt having a plurality of holes therethrough from which air is suctioned by a suction member disposed below the feeding belt to reduce edge floating. However, with this technique smaller sized sheets cannot be used because some of the air suctioned by the air suction member passes through holes in the feeding belt that are not covered by the smaller sized sheet. As a result, the suction force on the sheet is insufficient to smoothly feed the sheet by such a sheet feeding device.